Mr. Young centers on child prodigy Adam Young, who graduated from high school at the age of 9 and from university at the age of 14. Having missed the real high school experience, he decides to go back to his former high school as the science teacher. He re-unites with childhood best friend Derby, encounters the school bully Slab, and gets a crush on a student in his class named Echo. All of which makes it his social life that's being put to the test.